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All sources NASA NTRS DOE OSTI

DOE OSTI2026

Operation-Induced BiVO4 Surface Reconstruction Modulates Photoelectrochemical Glycerol Photooxidation Stability and Activity

Abstract Operation-induced surface reconstruction of photoelectrodes is underexplored as a path to control stability and performance. We show how adaptive junctions form via surface reconstruction of BiVO4 during glycerol photooxidation and how these surfaces affect electrolyte-dependent kinetics and durability. Preferential V dissolution in both acidic and alkaline media forms a Bi-rich layer. In situ measurements through a dual-working-electrode platform quantify the changes in photovoltage and charge-transfer resistance derived from adaptive junction formation, while enabling quantitative separation of the driving forces for charge separation and interfacial catalysis. The reconstructed surface in acidic media improves hole-transfer kinetics, functions as a glycerol-oxidation catalyst, and imparts photostability. Surface reconstruction in alkaline media exhibits the opposite behavior, impeding hole injection. This instability is mitigated by trace Ni2+ ions, which drive in situ surface activation without cocatalyst pre-deposition. This study shows the significance of surface reconstruction in the design of durable photoelectrodes for applications targeting organic electro-oxidation.

Yang, Jin Wook↗

NASA NTRS1999

Nitric-oxide synthase is a mechanical signal transducer that modulates talin and vinculin expression

Mechanical stimuli can cause changes in muscle mass and structure which indicate that mechanisms exist for transducing mechanical stimuli into signals that influence gene expression. Myotendinous junctions show adaptations to modified muscle loading which suggest that these are transcriptionally distinct domains in muscle fibers that may experience local regulation of expression of structural proteins that are concentrated at these sites. Vinculin and talin are cytoskeletal proteins that are highly enriched at myotendinous junctions that we hypothesize to be subject to local transcriptional regulation. Our findings show that mechanical stimulation of muscle cells in vivo and in vitro causes an increase in the expression of vinculin and talin that is mediated by nitric oxide. Furthermore, nitric oxide-stimulated increases in vinculin and talin expression occur through a protein kinase G-dependent pathway and therefore differ from other mechanisms through which nitric oxide has been shown previously to modulate transcription. Analysis of vinculin mRNA distribution in mechanically stimulated muscle fibers shows that the mRNA is highly concentrated at myotendinous junctions, which supports the hypothesis that myotendinous junctions are distinct domains in which the expression of cytoskeletal proteins is modulated by mechanical stimuli through a nitric oxide and protein kinase G-dependent pathway.

NASA Discipline Musculoskeletal↗

DOE OSTI2021

Controllable Reset Behavior in Domain Wall–Magnetic Tunnel Junction Artificial Neurons for Task-Adaptable Computation

Neuromorphic computing with spintronic devices has been of interest due to the limitations of CMOS-driven von Neumann computing. Domain wall–magnetic tunnel junction (DW-MTJ) devices have been shown to be able to intrinsically capture biological neuron behavior. Edgy-relaxed behavior, where a frequently firing neuron experiences a lower action potential threshold, may provide additional artificial neuronal functionality when executing repeated tasks. In this letter, we demonstrate that this behavior can be implemented in DW-MTJ artificial neurons via three alternative mechanisms: shape anisotropy, magnetic field, and current-driven soft reset. Using micromagnetics and analytical device modeling to classify the Optdigits handwritten digit dataset, we show that edgy-relaxed behavior improves both classification accuracy and classification rate for ordered datasets while sacrificing little to no accuracy for a randomized dataset. This letter establishes methods by which artificial spintronic neurons can be flexibly adapted to datasets.

42 ENGINEERING↗

DOE OSTI2024

Tailoring Interfaces for Enhanced Methanol Production from Photoelectrochemical CO 2 Reduction

Efficient and stable photoelectrochemical reduction of CO 2 into highly reduced liquid fuels remains a formidable challenge, which requires an innovative semiconductor/catalyst interface to tackle. In this study, we introduce a strategy involving the fabrication of a silicon micropillar array structure coated with a superhydrophobic fluorinated carbon layer for the photoelectrochemical conversion of CO 2 into methanol. The pillars increase the electrode surface area, improve catalyst loading and adhesion without compromising light absorption, and help confine gaseous intermediates near the catalyst surface. The superhydrophobic coating passivates parasitic side reactions and further enhances local accumulation of reaction intermediates. Upon one-electron reduction of the molecular catalyst, the semiconductor–catalyst interface changes from adaptive to buried junctions, providing a sufficient thermodynamic driving force for CO 2 reduction. These structures together create a unique microenvironment for effective reduction of CO 2 to methanol, leading to a remarkable Faradaic efficiency reaching 20% together with a partial current density of 3.4 mA cm –2 , surpassing the previous record based on planar silicon photoelectrodes by a notable factor of 17. Furthermore, this work demonstrates a new pathway for enhancing photoelectrocatalytic CO 2 reduction through meticulous interface and microenvironment tailoring and sets a benchmark for both Faradaic efficiency and current density in solar liquid fuel production.

14 SOLAR ENERGY↗

DOE OSTI2026

Nanometer Scale Imaging to Develop Quantitative Descriptors of Bipolar Membrane Junction Structure

Swings in pH can be achieved by electrically polarizing a bipolar membrane (BPM) to drive water dissociation at the BPM junction for electrochemical conversion and separation processes. BPM junction design is critical to tailor performance for specific applications; however, characterization techniques capable of resolving the nanometer scale physical structure of the junction are limited. We present sample preparation, imaging, and analysis workflows that are adaptable to a variety of BPM junction architectures. Atomic force microscopy produces BPM junction images with nanometer scale lateral resolution for samples with and without a graphene oxide water dissociation catalyst in the junction. Subsequent image segmentation and analysis quantify line edge roughness and catalyst layer thickness as descriptors of junction structure. Comparison of pre- and post-electrodialysis junctions suggests electric field-induced alignment of catalyst particles during electrodialysis. This characterization workflow can inform manufacturing protocols, computational modeling, and failure mode analysis for next-generation BPMs.

97 MATHEMATICS AND COMPUTING↗

NASA NTRS2012

Apparatus and method of manufacture for an imager equipped with a cross-talk barrier

An imager apparatus and associated starting material are provided. In one embodiment, an imager is provided including a silicon layer of a first conductivity type acting as a junction anode. Such silicon layer is adapted to convert light to photoelectrons. Also included is a semiconductor well of a second conductivity type formed in the silicon layer for acting as a junction cathode. Still yet, a barrier is formed adjacent to the semiconductor well. In another embodiment, a starting material is provided including a first silicon layer and an oxide layer disposed adjacent to the first silicon layer. Also included is a second silicon layer disposed adjacent to the oxide layer opposite the first silicon layer. Such second silicon layer is further equipped with an associated passivation layer and/or barrier.

Pain, Bedabrata↗

DOE OSTI2020

Constructing an Adaptive Heterojunction as a Highly Active Catalyst for the Oxygen Evolution Reaction

Electrochemical water splitting is of prime importance to green energy technology. Particularly, the reaction at the anode side, namely the oxygen evolution reaction (OER), requires a high overpotential associated with O—O bond formation, which dominates the energy-efficiency of the whole process. Activating the anionic redox chemistry of oxygen in metal oxides, which involves the formation of superoxo/peroxo-like (O 2 ) n – , commonly occurs in most highly active catalysts during the OER process. Here, a highly active catalyst is designed: electrochemically delithiated LiNiO 2 , which facilitates the formation of superoxo/peroxo-like (O 2 ) n – species, i.e., NiOO*, for enhancing OER activity. The OER-induced surface reconstruction builds an adaptive heterojunction, where NiOOH grows on delithiated LiNiO 2 (delithiated-LiNiO 2 /NiOOH). At this junction, the lithium vacancies within the delithiated LiNiO 2 optimize the electronic structure of the surface NiOOH to form stable NiOO* species, which enables better OER activity. This finding provides new insight for designing highly active catalysts with stable superoxo-like/peroxo-like (O 2 ) n – for water oxidation.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Quantized electronic transitions in electrodeposited copper indium selenide nanocrystalline homojunctions

Pairing semiconductors with electrochemical processing offers an untapped opportunity to create novel nanostructures for practical devices. Here we report the results of one such pairing: the in-situ formation of highly-doped, interface-matched, sharp nanocrystalline homojunctions (NHJs) with single step electrodeposition of two copper-indium-selenide (CISe) compounds on flexible foil. It produces a homogenous film, comprising inherently ordered, 3-dimensional interconnected network of pn -CISe NHJs. These CISe NHJs exhibit surprising non-linear emissions, quantized transitions, large carrier mobility, low trap-state-density, long carrier lifetime and possible up-conversion. They facilitate efficient separation of minority carriers, reduce recombination and essentially function like quantum materials. This approach mitigates the material issues and complex fabrication of incumbent nanoscale heterojunctions; it also overcomes the flexibility and scale-up challenges of conventional planar pn junctions. The self-stabilized CISe NHJ film can be roll-to-roll processed in ambient atmosphere, thus providing a promising platform for a range of optoelectronic technologies. This concept exemplified by CISe compounds can be adapted to create nano-scale pn junctions with other inorganic semiconductors.

36 MATERIALS SCIENCE↗

NASA NTRS1992

Comparative study of MacCormack and TVD MacCormack schemes for three-dimensional separation at wing/body junctions in supersonic flows

A robust, discontinuity-resolving TVD MacCormack scheme containing no dependent parameters requiring adjustment is presently used to investigate the 3D separation of wing/body junction flows at supersonic speeds. Many production codes employing MacCormack schemes can be adapted to use this method. A numerical simulation of laminar supersonic junction flow is found to yield improved separation location predictions, as well as the axial velocity profiles in the separated flow region.

Lakshmanan, Balakrishnan↗

NASA NTRS1966

O-rings with mylar back-up provide high- pressure cryogenic seal

Mylar lip type back-up ring installed in combination with three rubber O-rings seal the junctions between a tube stub and an adapter during high pressure gas flow at cryogenic to room temperatures. Mylar seals should not be used with oxygen under pressure or in the liquid state.

Funk, G. M.↗

DOE OSTI2026

A cell-centered AMR-ALE framework for 3D multi-material hydrodynamics. Part II: linesweep ALE rezoning for nonconformal block-structured AMR meshes

The simulation of flows presenting contact discontinuities, vorticity, and large variations in spatial scales can be performed in a framework coupling Arbitrary Lagrangian Eulerian (ALE) algorithms and Adaptive Mesh Refinement (AMR). This coupling requires adaptation of ALE rezoning techniques to meshes containing nonconformal nodes arising from both the AMR topology and the junction of mesh blocks. Here, in this paper, we present an ALE rezoning strategy that is compatible with such meshes, and that can also act as a disentangling algorithm. Emphasis is put on an algorithm that respects intrinsic Lagrangian mesh properties in order to preserve accuracy around discontinuities. To that end, we adapt the weighted linesweep algorithm to nonconformal block-structured AMR meshes. Then, we present control parameters introduced in the method for it to be applicable in practical situations. Notably, the method is coupled to a specific metric optimization in order to palliate some shortcomings of the linesweep method. Finally, numerical test cases are presented that feature the capabilities of the ALE-AMR algorithm for flows that present discontinuities, vorticity, and a variety of scales. Notably, we show that our ALE-AMR algorithm gives results at least similar to Euler-AMR, but provides better accuracy in cases where discontinuities are involved, thanks to a method that respects the Lagrangian features of the mesh. Additionally, it enables Euler-AMR-like computations on domains with temporally varying domain boundaries.

Adaptive mesh refinement↗

NASA NTRS2015

CarbAl Heat Transfer Material

The increasing use of power electronics, such as high-current semiconductor devices and modules, within space vehicles is driving the need to develop specialty thermal management materials in both the packaging of these discrete devices and the packaging of modules consisting of these device arrays. Developed by Applied Nanotech, Inc. (ANI), CarbAl heat transfer material is uniquely characterized by its low density, high thermal diffusivity, and high thermal conductivity. Its coefficient of thermal expansion (CTE) is similar to most power electronic materials, making it an effective base plate substrate for state-of-the-art silicon carbide (SiC) super junction transistors. The material currently is being used to optimize hybrid vehicle inverter packaging. Adapting CarbAl-based substrates to space applications was a major focus of the SBIR project work. In Phase I, ANI completed modeling and experimentation to validate its deployment in a space environment. Key parameters related to cryogenic temperature scaling of CTE, thermal conductivity, and mechanical strength. In Phase II, the company concentrated on improving heat sinks and thermally conductive circuit boards for power electronic applications.

Fink, Richard↗

DOE OSTI2024

DC Microgrid Reliability Enhancement with Adaptive Converter Thermal Management

Due to the different device selections, aging levels, and thermal dissipation performance, some converters may take additional thermal stress on switching devices than others in paralleled converter systems, which will reduce system reliability. To address this problem, this paper proposes a power-sharing strategy with adaptive thermal management. First, the temperature-based power loss model and electrical-thermal model are established. Based on that, a high-accuracy IGBT junction temperature estimate considering the power loss-temperature coupling can be achieved. Further, the thermal-sharing for all the switching devices in paralleled converters can be achieved with the proposed adaptive thermal management strategy. The proposed strategy can change the power-sharing ratio adaptively according to the system operation conditions, which will contribute to the system reliability enhancement. The effectiveness of the proposed strategy is verified through PLECS thermal simulation and joint real-time simulation with Dspace and RT-box.

DC microgrid↗

NASA NTRS2017

Metallic Junction Thermoelectric Device Simulations

Thermoelectric junctions made of semiconductors have existed in radioisotope thermoelectric generators (RTG) for deep space missions, but are currently being adapted for terrestrial energy harvesting. Unfortunately, these devices are inefficient, operating at only 7% efficiency. This low efficiency has driven efforts to make high-figure-of-merit thermoelectric devices, which require a high electrical conductivity but a low thermal conductivity, a combination that is difficult to achieve. Lowered thermal conductivity has increased efficiency, but at the cost of power output. An alternative setup is to use metallic junctions rather than semiconductors as thermoelectric devices. Metals have orders of magnitude more electrons and electronic conductivities higher than semiconductors, but thermal conductivity is higher as well. To evaluate the viability of metallic junction thermoelectrics, a two dimensional heat transfer MATLAB simulation was constructed to calculate efficiency and power output. High Seebeck coefficient alloys, Chromel (90%Ni-10%Cr) and Constantan (55%Cu-45%Ni), produced efficiencies of around 20-30%. Parameters such as the number of layers of junctions, lateral junction density, and junction sizes for both series- and parallel-connected junctions were explored.

Duzik, Adam J.↗

DOE OSTI2022

Real-time Condition Monitoring of Power Modules in Grid-tied Power Converter

This paper proposes and demonstrates a real-time condition monitoring method using gate driver integrated sensing circuits and sensor fusion algorithms. Power device on-state voltage (VDSon) measurement and junction temperature (Tj) sensing circuits with high noise immunity are built and integrated into an adaptive gate driver circuit for power modules. Considering the inherently noisy measurement environment of power converters, VDSon together with several other measurements are fused together to provide accurate descriptions of the stress and degradation of each power device. Furthermore, the gate driver circuit can actively control the turn-on gate voltage (VGSon) for each device based on the stress and degradation state. The proposed sensing circuits and power device condition assessment algorithms are implemented in a 75 KVA grid-tied power converter. This paper focuses on the sensing circuits hardware designs and testing in grid-tied power converter prototype and device stress index generation. More comprehensive results on the device state of health index generation will be presented in future work.

Fan, Junchong↗

NASA NTRS2022

A Novel High-Performance Mission-Enabling Multi-Purpose Radioisotope Heat Source

Recent studies indicate science mission concepts targeting access to the sub-surface oceans of icy moons require ice-penetrating cryobots powered by advanced Radioisotope Power Systems (RPS). These systems would deliver waste heat for ice-melting in the range of 10 kW. Minimizing the transit time through the kilometers-thick ice shells to just a few years requires these RPS to utilize heat sources having a higher thermal energy volumetric density than the existing flight-qualified General-Purpose Heat Source (GPHS). A Compact Heat Source (CPHS)has been conceptualized in which the graphite impact shells(GIS) of the existing GPHS are rearranged in a hexagonal aeroshell containing seven GIS per module, as opposed to the standard two per module; offering a thermal energy density of 0.57 W/cm3versus 0.29 W/cm3 offered by the GPHS simply from the repackaging of Technology Readiness Level (TRL)9 subassemblies. Preliminary thermal modeling of the CPHS integrated into a notional radioisotope thermoelectric generator(RTG) structure further suggests that centerline temperatures are well within allowable limits during nominal operation. Given the need for the CPHS for a subset of missions, it is worth exploring the applicability of the CPHS for more general RTG purposes. We discuss herein how the CPHS may be implemented with either heritage or in-development thermoelectric converter technologies into a Next-Generation RTG concept. Due to a higher energy density, the legacy heat rejection fin arrangement must be modified to permit a sufficiently low cold-side temperature. Preliminary finite element analysis suggests fin-root temperatures can be kept as low as 520 K while allowing the generator to fit within the usable dimensions of currently available United States Department of Energy shipping containers. Such temperatures would certainly be compatible with the use of high temperature thermoelectric converter technologies.. A prime candidate is the heritage silicon-germanium (SiGe) unicouple, whose design could be adapted by approximately halving the leg-length, but without changes in hot and cold junction interfaces, which are features critical to the proven performance and reliability of these devices. The estimated Beginning of Life power for a SiGe-based CPHS-RTG using 12 CPHS for a thermal inventory of 10.5 kW is greater than 600 W under deep space operating conditions. Using higher performance segmented couples currently in development that are based on skutterudite,La3−xTe4and 14-1-11 Zintl thermoelectric materials in lieu of the SiGe unicouples would increase the power level to more than1 kW. The high specific power (We/kg) attribute of CPHS-RTGs found in this study could potentially enable Radioisotope Electric Propulsion (REP) mission concepts. Past NASA REP mission concept studies identified specific power needs in excess of 6to 8 We/kg. Based on a GPHS-RTG-like system configuration, we show that at fin root temperatures between 530 K and 570K (deep space environment), specific powers exceeding 10 We/kg are achievable using high performance segmented thermoelectric converters. The compact sizing and power density of the CPHS-RTG would constitute a significant step upgrade in specific power when compared to heritage GPHS-RTG (approximately5.1 We/kg) and off-the-shelf Multi-Mission RTG (approximately 2.6 We/kg).

Nesmith, Bill J.↗

NASA NTRS1996

Response of the neuromuscular unit to spaceflight: what has been learned from the rat model

Despite the inherent limitations placed on spaceflight investigations, much has been learned about the adaptations of the neuromuscular system to weightlessness from studies of rats flown for relatively short periods (approximately 4-22 days). Below is a summary of the major effects of spaceflight observed in muscles of rats that are not in their rapid growth stage: 1. Skeletal muscles atrophy rapidly during spaceflight; significant atrophy is observed as early as after 4 days of flight. 2. The atrophic response appears to be related to the primary function of the muscle. In the hindlimb, the relative amount of atrophy can be characterized as slow extensors > fast extensors > fast flexors. This pattern of relative atrophy does not appear to be occurring in the forelimb; however, not enough data are available to draw any definitive conclusions at this time. 3. Both slow and fast fibers atrophy during spaceflight, with the largest fibers within an individual muscle generally showing the greatest atrophic response. Interestingly, the amount of fiber atrophy appears to reach a plateau after about 14 days of flight. 4. Adaptations have been observed in the concentration and content of all muscle proteins pools, with the protein pools in slow muscles the most affected. 5. Some slow and fast fibers in predominantly slow and fast muscles show shifts in their histochemical and biochemical properties, toward those observed in a "faster" phenotype. 6. Some fibers, presumably expressing slow MHC isoforms before flight, begin to express fast MHC isoforms during flight. 7. The oxidative capacity of the muscles or fibers is relatively unaffected by spaceflight, particularly in the slow muscles. Any change in whole-body fatigability associated with spaceflight most likely reflects the loss in muscle and fiber mass. 8. The glycolytic capacity of the muscles and muscle fibers is enhanced after spaceflight. This metabolic adaptation seems to be related to the shift in the contractile proteins towards "faster" isoforms. 9. The vascularity of muscles appears to be maintained after flight, based, at least, on histological observations of capillarity. 10. The force capabilities of the muscles and fibers appear to decrease in parallel with the decreases in size, i.e., the specific tension is not significantly affected after flight. 11. Changes in the speed-related properties of the slow muscles are consistent with the adaptations in the myosin molecule, i.e., the slow muscles and some fibers in the slow muscles become "faster." 12. Some muscle fiber and neuromuscular junction damage has been observed after flight, particularly in the slow muscles. The extent of damage may be related to the amount of time that the muscles are allowed to reload before removal, i.e., in general, shorter intervals result in less fiber damage. 13. Adaptations in the motor (ventral horn) and sensory (spinal ganglia) neurons have been quite variable, but this may be related to the amount of time that the muscles are allowed to reload before removal. Morphological adaptations after relatively short periods of reloading may reflect a decrease in the activation of the neural elements during flight.

manned↗

NASA NTRS2001

The Effect of Cytidine on the Structure and Function of an RNA Ligase Ribozyme

A cytidine-free ribozyme with RNA ligase activity was obtained by in vitro evolution, starting from a pool of random- sequence RNAs that contained only guanosine, adenosine, and uridine. This ribozyme contains 74 nt and catalyzes formation of a 3',5' -phosphodiester linkage with a catalytic rate of 0.016/min. The RNA adopts a simple secondary structure based on a three-way junction motif, with ligation occurring at the end of a stem region located several nucleotides away from the junction. Cytidine was introduced to the cytidine-free ribozyme in a combinatorial fashion and additional rounds of in vitro evolution were carried out to allow the molecule to adapt to this added component. The resulting cytidine-containing ribozyme formed a 3',5' linkage with a catalytic rate of 0.32/min. The improved rate of the cytidine-containing ribozyme was the result of 12 mutations, including seven added cytidines, that remodeled the internal bulge loops located adjacent to the three-way junction and stabilized the peripheral stem regions.

Rogers, Jeff↗